Section III Wind Turbines

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Section IIIWind Turbines

• Types of turbines
• Relative merits of each type
• General structure of turbines

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Big Wind/Small Wind Definition

• By common practice, small wind is defined as
  nameplate power rating of 100 kW or less.
• Large wind is considered to be for turbines with
  a nameplate rating greater than 100 kW.
• Sometimes a further refinement of turbine
  classifications occurs into small, intermediate,
  and large.

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Sizes and Applications

• Small (?10 kW)
• Homes
• Farms
• Remote Application

• Intermediate
• (10-250 kW)
• Village Power
• Hybrid Systems
• Distributed Power

• Large (660 kW - 2MW)
• Central Station Wind Farms
• Distributed Power
• Community Wind

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Wind Turbines

• Horizontal Axis, HAWT (all large power turbines
  are this type)
• Upwind
• Downwind

Wind Direction
Wind Direction
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Turbine Types
Wind Direction

• Vertical Axis, VAWT
• Good for low wind and turbulent wind (near ground)

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Worlds Largest Turbines

• Enercon E-126
• Rotor diameter of 126 m (413 ft)
• Rated at 6 MW, but produces 7 MW

• Clipper (off-shore)
• Rotor diameter of 150 m (492 ft)
• Hub Height is 328 ft
• Rated at 7.5 MW

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Typical Utility Scale Turbine in 2011

• Clipper 2.5 MW
• Hub height 80 m (262 ft)
• Rotor diameter 99 m (295 ft)
• 4 PM generators in one nacelle
• 3.28 ft/m

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• Vestas 1.65 MW turbines at NPPDs Ainsworth wind
  farm
• Class 5 wind site (average wind speed is 19.5
  mph)
• 36 turbines in farm
• Hub height is 230 feet
• Rotor diameter is 269 feet
• Project cost was about 1,355/kW (1.36/W)

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Small Wind Turbine

• Bergey Excel 10 kW
• Hub height 18-43 m (59-140 ft)
• Rotor diameter 7 m (23 ft)

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• 2.4 kW Skystream bySouthwest Wind Power
• Hub height is 45-60 ft.
• Rotor diameter is 12 ft.
• Installation cost is about 7 to 8.50 per Watt

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Major types of VAWT
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VAWT

• 30 m Darrieus
• Helical Twist

VAWT are designed to operate near the ground
where the wind power is lower and produce
drag on the trailing blades as they rotate
through the wind.
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Vertical axis turbines

• PacWind Seahawk, 500 W
• - Drag type
• PacWind Delta I, 2 kW
• Lift type
• Darius turbine, few 10s kW
• Lift type

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Lift and Drag

• Lift turbines are those that have the blades
  designed as air foils similar to aircraft wings.
  The apparent wind creates lift from a pressure
  differential between the upper and lower air
  surfaces.
• Lift turbines are much more efficient that drag
  type turbines
• Drag turbines operate purely by the force of the
  wind pushing the blade.

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Lift and Drag

• All utility-scale wind turbines are lift devices.
• All small turbines (HAWT or VAWT) that produce
  power efficiently are lift devices.
• Drag-type devices are Yard-Art
• In Drag-type turbines, Power transfer from the
  wind maximizes at about 8.1
• Compare to the Betz Limit of 59 for Lift
  devices

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HAWT

• We will focus on HAWT because these designs
  generally give better performance than VAWT

All further discussion relates to lift turbines
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• Nacelle
• The nacelle houses the generator, sometimes a
  gearbox, and often power electronics converters
  and control electronics.

Electrical Disconnect Switch
Tower
Foundation
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Typical foundation for turbines rated 1 to 5 kW
mounted on monopole towers.
Bolt set being placed into foundation pit prior
to concrete pour.
Conduit for electrical connection between turbine
and disconnect switchgear.
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Tower section (base) for large HAWT
Note the large number of bolt holes as compared
to the small turbine on the previous slides
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W is the angular velocity of the rotor tip in
units of radians/second
R is the blade length plus the rotor radius
Wind Direction with velocity, v
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Exercise 6

• 1). The two major types of turbines as designated
  by the orientation of their axis of rotation of
  the blades are
• 2-bladed or 3-bladed
• Upwind and Downwind
• Vertical and Horizontal
• Lift and Drag

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Exercise 6

• 2). A Drag-type turbine can capture more of the
  available power in the wind than a Lift-type.
• True
• False

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Exercise 6

• 3). Which of the following statements are true.
• Horizontal-axis turbines are generally used for
  large wind farms instead of Vertical-axis
  turbines.
• Lift-type turbines are always Horizontal-axis
  types.
• Wind turbines can be designed to face up into the
  wind or point downwind.
• B. and C.
• A. and C.
• A., B., and C.

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Physics Continued

• Tip Speed Ratio, l, is the ratio of the blade-tip
  speed (linear velocity) to wind speed.
• l WR/v
• W is the angular velocity of the rotor
• R is the radius of the rotor
• v is the wind velocity

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Power Coupled to Turbine from the Wind

• The Power Coefficient, Cp, is the percentage of
  the available power in the wind coupled into the
  turbine. Therefore, the Turbine Power, P, is
• P Cp Pw Cp (½ rAv3)
• The Power Coefficient, Cp, is a maximum
  (approaches Betz Limit) when the Tip Speed Ratio
  is in the range of 7.5 to 10.
• l is actively controlled in large turbines
• l is passively controlled in small turbines
  often through blade flexure

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Power Coefficient

• In modern turbines, the power coefficient Cp is
  around 40 (0.40).
• Remember the Betz Limit is about 59.

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Pitch and Yaw

• Pitch refers to the relative angle of the turbine
  blades to the incoming wind direction.

Apparent Wind Direction
Yaw is the direction of rotation of the turbine
nacelle and rotor assembly as it pivots around
the tower to move into or out of the wind.
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Turbine Output

• Modern turbines are around 90 or more efficient
  once the power is coupled to the rotor shaft.
• Reputable manufacturers will provide output power
  data at various wind speeds. Often these are
  provided as graphical plots.

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Turbine Power Curve

• The output power flattens out to a relatively
  constant value that the power electronics
  converter system, generator, and mechanical
  systems are designed to handle.

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Why does the Power Curve Peak and then Lay Over?
Ideally, Power goes as v3
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Blade positioning is actively or passively
controlled to limit the power output from the
turbine.

• Power curve can be made smooth by active control
  (active stall or pitch for large turbines)
• Passive Stall control has an overshoot depending
  on blade design (small turbines)

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Turbine Speed Specifications

• Cut-in Wind Speed is the wind velocity at which
  the turbine will begin to generate electrical
  power. (3 to 4 m/s are typical)
• Rated Wind Speed is the wind velocity at which
  the turbine will generate its nameplate
  electrical power. (12 to 15 m/s are typical)
• Cut-Out Wind Speed is the wind velocity at which
  the turbine will shut itself down to keep the
  electrical and mechanical systems safe. (25 m/s
  or 60 mph is typical)
• Survival Wind Speed is the wind velocity maximum
  at which the turbine can mechanically survive
  intact. (60 to 65 m/s is typical 140 mph)

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Cut-in Wind Speed
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Rated Wind Speed
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Cut-out Wind Speed
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Real Turbines with Measured Performance
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Exercise 7

• 1). A cut-in wind speed is likely to be about
• 12.5 m/s
• 30 m/s
• 42.5 m/s
• 3.5 m/s

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Exercise 7

• 2). Using the power curve from the Skystream 3.7
  above, what is the expected power production at
  a wind speed of 7.5 m/s?

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Exercise 7

• 3). Pitch refers to the orientation with respect
  to the apparent wind of what?
• The Blades
• The Nacelle
• The Rotor
• The Tower

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Exercise 7

• 4). Yaw refers to the orientation of what?
• The Blades
• The Nacelle
• The Rotor
• The Tower

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Exercise 7

• 5). The turbine does the best job of capturing
  the available wind power when the tip speed ratio
  is
• 2.3 kW
• 8
• 14 m/s
• 2

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Exercise 7

• 6). A turbines output power is controlled in
  high winds by
• Lift or Drag Control
• Upwind or Downwind Control
• Pitch or Stall Control
• Rotor or Yaw Control

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Operations and Maintenance Costs
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O M

• OM costs constitute a sizeable share of the
  total annual costs of a large wind turbine. For a
  new turbine, OM costs may easily make up 20-25
  of the total normalized cost per kWh produced
  over the lifetime of the turbine. If the turbine
  is fairly new, the share may only be 10-15, but
  this may increase to at least 20-35 by the end
  of the turbines lifetime. As a result, OM costs
  are attracting greater attention, as
  manufacturers attempt to lower these costs
  significantly by developing new turbine designs
  that require fewer regular service visits and
  less turbine downtime.
• OM costs are related to a limited number of cost
  components, including
• Insurance
• Regular maintenance
• Repair
• Spare parts, and
• Administration.
• Some of these cost components can be
  estimated relatively easily. For insurance and
  regular maintenance, it is possible to obtain
  standard contracts covering a considerable share
  of the wind turbines total lifetime. Conversely,
  costs for repair and related spare parts are much
  more difficult to predict. Although all cost
  components tend to increase as the turbine gets
  older, costs for repair and spare parts are
  particularly influenced by turbine age starting
  low and increasing over time.

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Small Turbine Maintenance

• Identify maintenance needs and implement service
  procedures for the tower, fasteners, guy cables,
  wind turbine, wiring, grounding system, lightning
  protection, batteries, power conditioning
  equipment, safety systems, and balance of system
  equipment.
• Measure system output and operating parameters,
  compare with specifications and expectations, and
  assess the operating condition of the system and
  components.
• If appropriate perform mechanical and electrical
  diagnostic procedures and interpret results.

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Example Skystream Turbine Maintenance

• From the ground, listen for abnormal sounds when
  the turbine is operating in moderate winds.
• Perform visual inspection from the ground at
  least once per year with turbine off.
• Check ground wire connection at tower and at
  grounding stake if possible
• Check for blade cracks or breaks (use binoculars)
• Check visually for damage to nacelle, nose, etc.

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Example of small business expenses from Ontario,
NY
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Exercise 8

• 1). Operations and Maintenance costs over the
  lifetime of a large turbine may easily be
• 5 of tower installation cost
• 1 to 2 of total lifetime costs
• Over 50 of total lifetime costs
• 20 to 25 of total lifetime costs

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Exercise 8

• 2). Which of the following are considered part of
  OM costs
• Repair
• Insurance
• Administration
• Foundation Excavation
• Spare Parts